Studies of AuNi alloys by electron spectroscopies with the aid of the line shape analysis by the pattern recognition method

The spectrum of electrons elastically backscattered from the surface and within its vicinity reflects the probability of electron elastic backscattering on the surface atoms, quasi‐elastic scattering and the inelastic scattering visible in the low energy side of the elastic peak. The method for investigating the processes of electron elastic backscattering on the surface atom is called the elastic peak electron spectroscopy (EPES). In the present work, AuNi alloys of different compositions are investigated using X‐ray photoelectron spectroscopy (XPS) and the EPES method with the aid of the line shape analysis called the fuzzy k‐nearest neighbour (fkNN) rule. The line shape analysis was found to be applicable for EPES spectroscopy. It allows distinguishing the surfaces exhibiting various surface roughness, texture and grain size, and quantifying the selected information depths. The quantitative results obtained from the XPS analysis and the EPES spectra line shape analysis indicated Au surface segregation with Au surface enriched profile. Quantitative discrepancies are discussed within the non‐uniform concentration profiles of constituents due to sputter cleaning and annealing, different diffusion coefficients for Au and Ni, differences in the information depths sampled by XPS and EPES methods and differences in electron elastic backscattering cross‐sections for Ni and Au. Copyright © 2006 John Wiley & Sons, Ltd.     

Interlaboratory study comparing analyses of simulated angle‐resolved X‐ray photoelectron spectroscopy data

An interlaboratory study has been conducted to determine the following: (i) the similarities and differences of film thicknesses and composition profiles obtained from analyses of simulated angle‐resolved X‐ray photoelectron spectroscopy (ARXPS) data by different analysts using different algorithms for data analysis, and (ii) the effects of two assumptions commonly made in data‐analysis algorithms for ARXPS on derived film thicknesses and composition profiles. The analyzed data were generated by the National Institute of Standards and Technology Database for the Simulation of Electron Spectra for Surface Analysis, (SESSA) which provides a simple way to study the influence of the aforementioned effects on compositional depth profile reconstruction. Sets of simulated ARXPS data were produced for thin films of SiO₂, SiON, HfO₂, and HfON of varying thicknesses on a Si substrate. For some HfON films, the N concentration varied with depth. Eleven groups participated in the round robin study. The majority (eight) employed a commercial ARXPS instrument in which the angular distribution is measured for a fixed sample geometry, in contrast to conventional ARXPS in which the sample is tilted for angular variation. The average deviations between the reported average depth, film thickness, and amount of material typically varied between 20% and 30% but were considerably larger, between 30% and 80%, for some cases. The average errors were generally larger for simulations that included elastic scattering and the finite analyzer‐acceptance angle (realistic conditions) than those for simulations that neglected elastic scattering and the finite analyzer‐acceptance angle (simplified conditions). The retrieved N depth profiles were quantitatively different from the true depth profiles and showed substantial variability among the group of members who used the same instrument and analysis software. Copyright © 2014 John Wiley & Sons, Ltd.     

Surface oxidation process of a diamond‐like carbon film analyzed by difference X‐ray photoelectron spectroscopy

Difference X‐ray photoelectron spectroscopy (D‐XPS) revealed the surface oxidation process of a diamond‐like carbon (DLC) film. Evaluation of surface functional groups on DLC solely by the C 1s spectrum is difficult because the spectrum is broad and has a secondary asymmetric lineshape. D‐XPS clarified the subtle but critical changes at the DLC surface caused by wet oxidation. The hydroxyl (C―OH) group was dominant at the oxidized surface. Further oxidized carbonyl (C?O) and carboxyl (including carboxylate) (COO) groups were also obtained; however, the oxidation of C?O to COO was suppressed to some extent because the reaction required C―C bond cleavage. Wet oxidation cleaved the aliphatic hydrogenated and non‐hydrogenated sp² carbon bonds (C―H sp² and C―C sp²) to create a pair of C―OH and hydrogenated sp³ carbon (C―H sp³) bonds. The reaction yield for C―H sp² was superior at the surface, suggesting that the DLC film was hydrogen rich at the surface. Oxidation of aromatic sp² rings or polycyclic aromatic hydrocarbons such as nanographite to phenols did not occur because of their resonance stabilization with electron delocalization. Non‐hydrogenated sp³ carbon (C―C sp³) bonds were not affected by oxidation, suggesting that these bonds are chemically inert. Copyright © 2014 John Wiley & Sons, Ltd.     

Summary of ISO/TC 201 Standard: XXIX. ISO 20903: 2006—Surface chemical analysis—Auger electron spectroscopy and X‐ray photoelectron spectroscopy—methods used to determine peak intensities and information required when reporting results

This article is a brief summary of the ISO Standard 20903. This standard provides information on methods for the measurement of peak intensities in Auger electron and X‐ray photoelectron spectra and on uncertainties of the derived peak areas. It also specifies the necessary information required in a report of analytical results based on such measurements. Published in 2007 by John Wiley & Sons, Ltd.     

Characterization of high‐aspect‐ratio periodic structures by X‐ray photoelectron spectroscopy

X‐ray photoelectron spectroscopy (XPS) is a powerful surface characterization technique often relied on for quantification of surface species and coverages. Investigation of silicon microrods, considered a model for high‐aspect‐ratio structures, at different angles with respect to substrate normal was determined to have a significant impact on the relative sensitivity of surface‐bound species on rods relative to the base substrate. Comparison between planar silicon and microrod arrays demonstrates that the angular dependence is complicated and that careful studies must optimize conditions to differentiate between surfaces. In addition, the use of reverse angle resolved XPS, where the substrate is turned away from the X‐ray source, is shown to assist in simplifying the spectrum by removing underlying signal from the substrate near the base. Copyright © 2016 John Wiley & Sons, Ltd.     

X‐ray photoelectron analysis of surface functional groups on diamond‐like carbon films by gas‐phase chemical derivatization method

Oxygen‐related surface functional groups on diamond‐like carbon (DLC) films were derivatized with fluorine‐ and nitrogen‐related groups by the gas‐phase chemical derivatization (GCD) method, and the groups were analyzed quantitatively by X‐ray photoelectron spectroscopy (XPS). It is desirable that a derivatization reaction is unique to the target group; however, it usually causes undesirable side reactions which affect other groups. This diversity of the reactions has complicated the analysis. In this report, we have overcome the problem by applying a mathematical treatment which takes the side reactions into account. This improved analysis shows that it is no longer necessary to have derivatization reactions unique to the target groups. As a result, it is demonstrated that the carbonyl (C?O) group is the dominant surface functional group on both the DLC and its wet‐oxidized films, the carboxyl (COOH) group plays a minor role, and the presence of the hydroxyl (OH) group is logically denied. Considering the oxidation steps of these oxygen‐related surface functional groups, it is suggested that the C?O group on the DLC films requires the cleavage of the carbon–carbon bond with a relatively high activation energy barrier to change into the COOH group. Copyright © 2010 John Wiley & Sons, Ltd.     

X‐ray photoelectron spectroscopic chemical state quantification of mixed nickel metal,oxide and hydroxide systems

Quantitative chemical state X‐ray photoelectron spectroscopic analysis of mixed nickel metal, oxide, hydroxide and oxyhydroxide systems is challenging due to the complexity of the Ni 2p peak shapes resulting from multiplet splitting, shake‐up and plasmon loss structures. Quantification of mixed nickel chemical states and the qualitative determination of low concentrations of Ni(III) species are demonstrated via an approach based on standard spectra from quality reference samples (Ni, NiO, Ni(OH)₂, NiOOH), subtraction of these spectra, and data analysis that integrates information from the Ni 2p spectrum and the O 1s spectra. Quantification of a commercial nickel powder and a thin nickel oxide film grown at 1‐Torr O₂ and 300 °C for 20 min is demonstrated. The effect of uncertain relative sensitivity factors (e.g. Ni 2.67 ± 0.54) is discussed, as is the depth of measurement for thin film analysis based on calculated inelastic mean free paths. Copyright © 2009 John Wiley & Sons, Ltd.     

XPS and XAES analysis of copper,arsenic and sulfur chemical state in enargites

Enargite, a copper arsenic sulfide with the formula Cu₃AsS₄ is of environmental concern due to its potential to release toxic arsenic species. The oxidation and dissolution of enargite are governed by the composition and chemical state of the outermost surface layer. Qualitative and quantitative analysis of the enargite surface can be initially obtained on the basis of X‐ray photoelectron spectroscopy (XPS) binding energy and intensity data. However, a more precise determination of the chemical state of the principal elements of enargite (copper, arsenic and sulfur) in the altered surface layer and in the bulk of the mineral requires a combined analysis based on XPS photoelectron lines and the corresponding X‐ray excited Auger lines. On the basis of results obtained on natural and synthetic enargite samples and on standards of sulfides and oxides, the Auger parameter α′ of different compounds was calculated and the Wagner chemical state plots were drawn for arsenic, copper and sulfur. Arsenic in enargite is found to be in a chemical environment similar to that of arsenides or elemental arsenic, whereas copper in enargite is in a chemical state that corresponds to copper sulfide, Cu₂S, for all samples irrespective of surface treatment (natural or freshly cleaved). Only sulfur changed from a chemical state similar to that of copper or iron sulfide in freshly cleaved samples to another state in natural enargite in the as‐received state. Thus, it is the sulfur atom at the surface of enargite that is most susceptible to changes in the enargite surface state and composition. A more detailed interpretation of this behavior, based on differences in the initial and final state effects, is proposed here. The concept of Auger parameter and chemical state plot, used here for the first time for investigating enargite, has proved to be a method to unambiguously assign the chemical state of the principal elements copper, arsenic and sulfur in these minerals. Copyright © 2006 John Wiley & Sons, Ltd.     

Summary of ISO/TC 201 Standard: XX ISO 18118: 2004 – Surface chemical analysis – Auger electron spectroscopy and X‐ray photoelectron spectroscopy – Guide to the use of experimentally determined relative sensitivity factors for the quantitative analysis of homogeneous materials

ISO 18118 provides guidance on the measurement and use of experimentally determined relative sensitivity factors for the quantitative analysis of homogeneous materials by Auger electron spectroscopy (AES) and X‐ray photoelectron spectroscopy (XPS). This article provides a brief summary of this International Standard. Copyright © 2005 John Wiley & Sons, Ltd.     

Summary of ISO/TC 201 standard: XXI. ISO 21270:2004—Surface chemical analysis—X‐ray photoelectron and Auger electron spectrometers—Linearity of intensity scale

This International Standard specifies two methods for determining the maximum count rate for an acceptable limit of divergence from linearity of the intensity scale of Auger and x‐ray photoelectron spectrometers. It also includes methods to correct for intensity non‐linearities so that a higher maximum count rate can be employed for those spectrometers for which the relevant correction equations have been shown to be valid. Copyright © 2004 John Wiley & Sons, Ltd.     

In situ ion beam sputter deposition and X‐ray photoelectron spectroscopy (XPS) of multiple thin layers under computer control for combinatorial materials synthesis

Deposition of ultra‐thin layers under computer control is a frequent requirement in studies of novel sensors, materials screening, heterogeneous catalysis, the probing of band offsets near semiconductor junctions and many other applications. Often large‐area samples are produced by magnetron sputtering from multiple targets or by atomic layer deposition (ALD). Samples can then be transferred to an analytical chamber for checking by X‐ray photoelectron spectroscopy (XPS) or other surface‐sensitive spectroscopies. The ‘wafer‐scale’ nature of these tools is often greater than is required in combinatorial studies, where a few square centimetres or even millimetres of sample is sufficient for each composition to be tested. The large size leads to increased capital cost, problems of registration as samples are transferred between deposition and analysis, and often makes the use of precious metals as sputter targets prohibitively expensive. Instead we have modified a commercial sample block designed to perform angle‐resolved XPS in a commercial XPS instrument. This now allows ion‐beam sputter deposition from up to six different targets under complete computer control. Ion beam deposition is an attractive technology for depositing ultra‐thin layers of great purity under ultra‐high vacuum conditions, but is generally a very expensive technology. Our new sample block allows ion beam sputtering using the ion gun normally used for sputter depth‐profiling of samples, greatly reducing the cost and allowing deposition to be done (and checked by XPS) in situ in a single instrument. Precious metals are deposited cheaply and efficiently by ion‐beam sputtering from thin metal foils. Samples can then be removed, studied and exposed to reactants or surface treatments before being returned to the XPS to examine and quantify the effects. Copyright © 2016 The Authors Surface and Interface Analysis Published by John Wiley & Sons Ltd.     

Encoding of stoichiometric constraints in the composition depth profile reconstruction from angle resolved X‐ray photoelectron spectroscopy data

The inversion of angle resolved XPS data is a difficult problem, due to mathematical complexity of accurate model of electron transport, sensitivity to noise and small number of measured points limiting the depth resolution and the accuracy of the calculated depth profiles. Extended maximum entropy model for the calculation of apparent compositions (measured intensity ratios) is presented which allows to encode linear relationship between element concentrations. These can be used to calculate a solution with additional stoichiometric relationships and analyze, simultaneously, signals from several synthetic peak components. The synthetic peak components used in the model can represent various core level energy shifts, which are otherwise difficult to determine unambiguously from the measured signal. Element concentrations linked with stoichiometric relationships are used to identify compound materials with known density and inelastic scattering properties. The new model, thus allows self‐consistent recovery of depth profiles using maximum entropy method without the assumption of homogeneous density. The improved accuracy of the recovered depth profiles is demonstrated on the analysis of HfON/SiON overlayers. Various artefacts in the depth profiles obtained with standard maximum entropy model, which assumes constants density are identified. Copyright © 2011 John Wiley & Sons, Ltd.     

Summary of ISO/TC201 technical report: ISO/TR 18392: 2005—Surface chemical analysis—X‐ray photoelectron spectroscopy—Procedures for determining backgrounds

ISO Technical Report 18392 provides the guidance for determining backgrounds in X‐ray photoelectron spectra. The methods of background determination described in this report are applicable for the quantitative evaluation of the spectra of photoelectrons and Auger electrons excited by X‐rays from solid surfaces and surface nanostructures. Copyright © 2006 John Wiley & Sons, Ltd.     

Determination of ZnO(0001) surface termination by x‐ray photoelectron spectroscopy at photoemission angles of 0° and 70°

We present an XPS method to determine the termination of the ZnO(0001) surface. By measuring O 1s and Zn 2p_3/2 core‐level x‐ray photoelectron spectra at photoemission angles of 0° and 70° and comparing the intensity ratio (I_O1s/I_Zn2p3)_θ=0/(I_O1s/I_Zn2p3)_θ=70, the Zn and O termination can be distinguished. Calculations show that these two terminations have intensity ratios differing by ～17%. This difference is not affected by a contamination layer provided that the contamination layer thickness is the same for these two differently terminated surfaces. Although this determination method prefers a clean ZnO(0001) surface (in situ measurement), it seems also feasible for surfaces with known contamination layer thickness (ex situ measurement). We have measured ex situ ZnO(0001)‐Zn, ZnO(000&1macr;)‐O single crystals and an epitaxial ZnO film deposited on Al₂O₃(0001). The measured intensity ratios of the first two samples agree with the calculated values for a 0.2 and 0.26 nm contamination layer, respectively. The intensity ratio and the O 1s contamination component intensity of the epitaxial ZnO film are close to those of the ZnO(0001)‐Zn single crystal thus pointing at Zn termination of the film. Copyright © 2004 John Wiley & Sons, Ltd.     

Summary of ISO/TC 201 Standard: ISO 14701:2011 – Surface chemical analysis – X‐ray photoelectron spectroscopy—measurement of silicon oxide thickness

This International Standard specifies several methods for measuring the oxide thickness at the surfaces of (100) and (111) silicon wafers as an equivalent thickness of silicon dioxide when measured using X‐ray photoelectron spectroscopy. It is only applicable to flat, polished samples and for instruments that incorporate an Al or Mg X‐ray source, a sample stage that permits defined photoelectron emission angles and a spectrometer with an input lens that may be restricted to less than a 6° cone semiangle. For thermal oxides in the range 1‐ to 8‐nm thickness, using the best method described in this International Standard, uncertainties at a 95% confidence level around 2% may be typical and around 1% at optimum. A simpler method is also given with slightly poorer, but often adequate, uncertainties. Copyright © 2012 Crown copyright.     

Photoelectron spectroscopy on organic surfaces: X‐ray degradation of oxygen‐plasma‐treated and chemically reduced poly(propylene) surfaces in comparison to conventional polymers

The X‐ray‐induced sample damage during mono XPS analysis of an oxygen‐plasma‐oxidized and subsequently wet‐chemically reduced poly(propylene) film was investigated as a showcase for plasma‐modified or plasma‐deposited samples. By doing this, the degradation index approach as introduced by Beamson and Briggs in the Scienta ESCA300 high‐resolution XPS database of organic polymers has been adopted. As to be expected, the sample degrades by loosing oxygen as revealed by observation of decreasing O/C and C OR/C_sum ratios. However, the X‐ray degradation indices are definitely higher than those of conventional reference polymers. Moreover, the C OR/C_sum degradation index is significantly higher in comparison with one obtained for the O/C ratio. In that context, there is no difference between the plasma sample and a conventional poly(vinyl alcohol) polymer. It is concluded that for reliable quantitative surface chemical analysis, the quality of spectra in terms of acquisition times must be optimized aimed to a minimization of X‐ray degradation. Finally, it is proposed to describe the photon flux of an X‐ray gun in an XPS experiment, which defines the degradation rate at the end, by using the sample current simply measured with a carefully grounded sputter‐cleaned reference silver sample. Copyright © 2009 John Wiley & Sons, Ltd.     

Infrared spectroscopic ellipsometry (IRSE) and X‐ray photoelectron spectroscopy (XPS) monitoring the preparation of maleimide‐functionalized surfaces: from Au towards Si (111)

The IR ellipsometric technique was used to identify the surface species and to control the preparation of maleimide‐terminated surfaces. Because of higher s/n ratios for metallic substrates, the protocol was initially developed on Au surfaces, was later successfully transferred to technologically more relevant Si (111) substrates. The functionalized surfaces were achieved by electrochemical deposition of diazonium linker films and following chemical adsorption steps. Complementary XPS was also employed to detect the surface species in the process of preparation. The immobilization of different functional molecules was proven by interpreting the specific vibrational bands in IR spectra and additionally confirmed by XPS experiments. The surface homogeneity was investigated by FT‐IR synchrotron mapping ellipsometry. This work shows that the proposed protocol is an effective pathway to achieve the desired functionalized surfaces. Copyright © 2010 John Wiley & Sons, Ltd.     

Quantitative analysis of trace levels of surface contamination by X‐ray photoelectron spectroscopy. Part II: Systematic uncertainties and absolute quantification

We discuss analyses of trace levels of surface contamination using X‐ray photoelectron spectroscopy (XPS). The problem of quantifying common sources of statistical and systematic uncertainties for these measurements is formulated in terms of the needs of extreme ultraviolet lithography, but the results and conclusions are applicable to a broad range of XPS applications. We quantify the systematic uncertainties introduced by particular cases of overlapping peaks on different substrate structures by simulating measured spectra with the National Institute of Standards and Technology Database for the Simulation of Electron Spectra for Surface Analysis (SESSA). One example demonstrates that the relative atomic concentrations of trace elements such as S, P, and halogens on a Ru surface could be dramatically overestimated if the fitting of the overlapping Ru 3d and C 1s peaks excludes the contribution from carbon. We also show how spectra generated by SESSA can be compared with measured spectra to determine absolute amounts of surface impurities on layered samples of the type used for extreme ultraviolet lithography. We provide estimates of the total uncertainty for such measurements by considering the systematic limitations of SESSA and the statistical uncertainties of the measurements. The same procedure can be employed for other multilayered materials. Finally, we describe two approaches for converting XPS detection limits for an elemental impurity in an elemental matrix to the corresponding detection limits for the impurity as a thin film on the surface of the matrix material.     

Quantitative analysis of trace levels of surface contamination by X‐ray photoelectron spectroscopy. Part I: Statistical uncertainty near the detection limit

We discuss the problem of quantifying common sources of statistical uncertainties for analyses of trace levels of surface contamination by using X‐ray photoelectron spectroscopy. We examine the propagation of error for peak‐area measurements by using common forms of linear and polynomial background subtraction including the correlation of points used to determine both background and peak areas. This correlation has been neglected in previous analyses, but we show that it contributes significantly to the peak‐area uncertainty near the detection limit. We introduce the concept of relative background subtraction variance (RBSV) that quantifies the uncertainty introduced by the method of background determination relative to the uncertainty of the background area itself. The uncertainties of the peak area and atomic concentration and of the detection limit are expressed using the RBSV, which separates the contributions from the acquisition parameters, the background‐determination method, and the properties of the measured spectrum. These results are then combined to find acquisition strategies that minimize the total measurement time needed to achieve a desired detection limit or atomic‐percentage uncertainty for a particular trace element. Minimization of data‐acquisition time is important for samples that are sensitive to X‐ray dose and also for laboratories that need to optimize throughput.     

Summary of ISO/TC 201 Technical Report: ISO/TR 19319: 2003—Surface chemical analysis—Auger electron spectroscopy and x‐ray photoelectron spectroscopy—Determination of lateral resolution,analysis area and sample area viewed by the analyser

ISO Technical Report 19319:2003 contains information on the determination of lateral resolution, analysis area and sample area viewed by the analyser in surface analyses by Auger electron spectroscopy and x‐ray photoelectron spectroscopy. This article provides a brief summary of this information. Copyright © 2004 John Wiley & Sons, Ltd.